fix(plugin): reload preview on external Stencil builds via staticDirs

[davidpett]

Summary

Two related fixes for the Stencil Storybook dev preview:

1. HMR for externally-built Stencil — reload the preview when a consumer builds Stencil via a separate stencil build --watch and serves the prebuilt output through Storybook staticDirs (e.g. staticDirs: ['../dist/esm']) with a lazy defineCustomElements() in preview.tsx.
2. No spurious reload on first preview load — pre-bundle the deps Storybook/Stencil otherwise discover lazily, so Vite doesn't run a mid-session dep re-optimization that tears down the iframe right as the first story renders.

1. External-build HMR

In the external-build / lazy setup, stories never import a component .tsx into Vite's module graph, so the injected unplugin-stencil never compiles the project and its dependency maps stay empty. On a rebuild the external stencil --watch rewrites dist/esm/*.js, but those are static assets Vite doesn't track as modules — so the existing eager / lazy / style reload paths in stencilPreviewReloadPlugin can't fire and the preview never reloads.

Changes in packages/plugin/src/preset.ts:

• Resolve the configured staticDirs to absolute paths in viteFinal (via options.presets.apply('staticDirs'), relative to configDir) and pass them to stencilPreviewReloadPlugin.
• Explicitly server.watcher.add() those dirs — dist/esm lives outside Vite's root, so chokidar won't watch it otherwise.
• On a *.js change inside a watched static dir, invalidate the cached dist/esm modules and send the existing stencil:reload event.
• Debounce the reload (one external rebuild rewrites many chunks), and skip it while a lazy in-graph rebuild is pending to avoid double reloads.

Auto-detected / opt-in: a no-op when no staticDirs are configured.

2. Pre-bundle deps to avoid mid-session reload

storybook/internal/docs-tools, @stencil/core, and @stencil/core/internal/client were discovered lazily on the first preview load, triggering Vite dep re-optimizations (optimized dependencies changed. reloading) that tore down the iframe as the first story rendered. This surfaced as a CI flake in the HMR e2e suite (the reload raced the initial <my-component> render) but also affects real users as a surprise full reload on first load.

• Add optimizeDeps.include for those deps so all optimization happens at startup and the preview renders once, without a reload.
• Harden the HMR e2e before hook (tests/hmr.e2e.ts) to re-enter the iframe and re-query across any reload, as defense-in-depth.

Test plan

• example-lazy (external stencil build --watch + staticDirs: ['../dist/esm']): preview renders with no startup reload; editing a component reloads the preview.
• example (eager, in-graph): editing a component/style reloads once (no double-fire / regression).
• No reloading messages observed in either suite after pre-bundling.
• CI build_and_test green.